A descriptive study on the adjacent segment degeneration related signs following a lumbar fusion procedure

Adjacent segment degeneration (ASD) is a frequent complication following vertebral fusion procedures and is defined as the condition where patients recover after the initial procedure but develop compatible symptoms with radiological injuries in the segments adjacent to the fused ones at a later stage. The objective of the study was to describe the frequency and analysis of ASD related signs following a lumbar fusion procedure.

Observational descriptive retrospective study on patients with degenerative or instability conditions, operated on by posterolateral or circumferential lumbar fusion procedure. Pedicle screws, interbody peek cages (polyether-ether-ketone) and autologous bone graft were used. Clinical (pain and disability) and radiological (instability, rotation, disc height loss, radiological degeneration evaluated by X-ray and MR) variables were analysed.

Postoperative disc height loss was observed in 159 free discs among 112 patients (42.6%) (95% CI: 36.4-48.8%). Anterior or posterior slippage (anterolisthesis or retrolisthesis) at the end of the follow-up period was observed in 33 patients (12.5%). Upper segment rotation increased in the postoperative period in 36 patients (13.6%). Radiological disc degeneration was observed in 107 discs among 72 patients, being more frequent in the immediate upper disc with grade 2 and 3 changes at the end of follow-up in 48 discs from 35 patients (13.6%) (95% CI: 13.4-23.1%). Radiological ASD signs were observed in 151 patients (57.4%; 95% CI: 51.2-63.6%) and 53 of them (20.2%; 95% CI: 15.1-25.2%) who also showed clinical ASD symptoms (clinical and radiological ASD). Degeneration changes with degrees IV and V shown by a preoperative and magnetic resonance (MR) study at end of the follow-up period performed in 73 patients (27.7%), were observed in 46 discs among 32 patients (43.8%) (95% CI: 31.8-55.9%).

Radiological ASD signs evaluated in every free disc following a lumbar fusion procedure are observed with a variable frequency. All free discs after fusion were assessed as they could indicate mechanisms of compensation of lordosis loss and should be taken into consideration in a prospective revision surgery.